Yes, the PC automatically assigns drive letters. The windows drive will get a C (but you don’t need to do anything). I’ll just add that after cloning, you’ll either need to temporarily disconnect the 250gb. Sometimes your PC won’t know which drive to boot from if you have two copies of windows attached (the 250gb and the 1tb). You can fix this later on by plugging in the 250gb externally and wiping it. But yeah, you don’t need to get hung up on drive letters, all that matters is that you have a hard drive with an OS like Windows for your computer to boot from. If you copy it over, and then start up your PC with the new copied drive attached, it should boot from it and that’ll become the new C drive.